1. Field of the Invention
The present invention relates to a cast product made of at least two different materials and, more particularly, a method for producing a compound cast product from different materials in a casting machine.
2. Description of the Prior Art
Component parts, such as automobile parts, are often used in circumstances where different portions of the component part are subjected to differing operating conditions. However, most casting apparatuses and methods for forming component parts yield cast structures that have similar, i.e., uniform, properties throughout. Thus, modulus of elasticity, strength, and other inherent properties of the component part do not vary significantly with location through the cast component part. However, it is often desirable to have different properties in different areas of a component part, such as the aforementioned automobile parts, which may be subjected to differing operating conditions. The following prior art references are known attempts to form component parts having different properties in different areas of the part.
U.S. Pat. No. 3,847,203 to Northwood discloses a sequential casting method for casting a component part made of two metal alloys. The component part is cast in a ceramic casting mold into which the two metal alloys are poured. In the method disclosed by the Northwood patent, a first metal alloy is poured into the casting mold and allowed to cool, but not completely solidify. Thereafter, a second metal alloy is poured into the casting mold on top of the first metal alloy and both metal alloys are allowed to cool. The resulting component part is thus formed of multiple metal layers.
U.S. Pat. No. 3,752,212 to Thompson discloses a similar xe2x80x9csequentialxe2x80x9d casting method to that disclosed by the Northwood patent for casting a component part made of two metal alloys. In the method disclosed by the Thompson patent, two different metals are poured into a casting mold in sequence. However, in the method disclosed by the Thompson patent the first poured metal alloy is permitted to cool and solidify before the second molten metal alloy is poured into the casting mold. The resulting component part is formed by multiple metal layers in a manner similar to the Northwood patent.
U.S. Pat. No. 5,762,969 to Shimmell discloses an apparatus for casting a tubular component part in multiple portions or layers. The casting apparatus disclosed by the Shimmell patent includes a mold assembly in which multiple xe2x80x9cshotsxe2x80x9d of molten metal are poured sequentially into a mold cavity of the casting apparatus, which ultimately results in a component part made of multiple layers of metal. The tubular article is formed in a rotatable centrifugal casting mold.
U.S. Pat. No. 5,000,244 to Osborne discloses a lost foam casting apparatus for producing an automobile engine block. The casting apparatus disclosed by the Osborne patent is gravity fed and includes two inlets for supplying two different molten aluminum alloys to the mold cavity of the casting apparatus. The engine block casting is made by a lost foam process that employs an expendable pattern formed of expanded polystyrene. The pattern defines a first runner system for casting a first aluminum alloy and a second runner system for casting a second aluminum alloy in the mold cavity. The first and second aluminum alloys are independently, but concurrently, cast into a singular mold such that the entire engine block pattern is duplicated and an integral casting is formed.
U.S. Pat. No. 5,579,822 to Darsy et al. discloses a method for producing cast cylinder heads made of two different aluminum alloys. The method disclosed by the Darsy et al. patent requires the sequential pouring of two different molten aluminum alloys into the mold cavity of a casting apparatus. The molten aluminum alloys, upon solidification, form a cast cylinder head made of different layers of aluminum alloy.
The foregoing references each generally utilize a gravity flow arrangement to induce multiple molten metal alloys into a mold cavity of a casting apparatus. With such gravity flow arrangements it is difficult to control the mixing of the different molten metal alloys as they are fed into the mold cavity. In addition, such gravity flow in the arrangements often cause air pockets to form in the mold cavity, which weakens the resulting cast component part. Further, the pouring of molten aluminum alloys, in particular, into a casting mold under the force of gravity, often causes formation of undesirable metal oxides in the molten aluminum alloys.
In view of the foregoing, it is an object of the present invention to provide a method and apparatus for producing a cast product from at least two different materials such that the resulting cast product has different properties in different areas of the product. In addition, it is an object of the present invention to provide a method and apparatus for producing a cast product from at least two different materials such that the properties of the resulting cast product may be optimized in different areas of the cast product.
The above objects are accomplished with a method for producing a unitary compound cast product in accordance with the present invention. The method is practiced with a casting mold having a mold cavity sized and shaped to form the cast product. The casting mold has a bottom side. A plurality of injectors is supported from the bottom side of the casting mold. The injectors are in fluid communication with the mold cavity through the bottom side of the casting mold. A molten material holder furnace is located beneath the casting mold. The holder furnace defines a molten material receiving chamber configured to separately contain supplies of the at least two different molten materials. The holder furnace is positioned such that the injectors extend downward into the receiving chamber. The receiving chamber is separated into at least two different flow circuits for the at least two different molten materials. A first molten material is received in a first flow circuit in the receiving chamber. A second molten material is received in a second flow circuit in the receiving chamber. The first and second molten materials remain isolated from each other while in the receiving chamber. The first and second molten materials are injected separately into the mold cavity with the injectors. The injectors inject the first and second molten materials upward into the mold cavity against the force of gravity.
The injectors preferably inject the first and second molten materials into different areas of the mold cavity. The two flows join to form an interface of varied composition. The transition between the two materials will be relatively sharp. The first and second molten materials are preferably allowed to solidify in the mold cavity to form the joined compound cast product as a unitary body. The compound cast product may then be removed from the mold cavity of the casting mold.
The first and second molten materials may be metal alloys having different metallurgical properties. In addition, the first and second molten materials may be aluminum-based alloys, which may contain ceramic particulates.
The injectors may be piston-cylinder injectors. Thus, the method of the present invention may include the step of injecting the first and second molten materials into the mold cavity during an upstroke of the piston directed toward the bottom side of the casting mold. The first flow circuit may connect a first plurality of the injectors in series to one another. Likewise, the second flow circuit may connect a second plurality of the injectors in series to one another.
The method of the present invention may be practiced using two or more different molten materials. Accordingly, the method may further include the steps of receiving a third molten material into a third flow circuit formed in the receiving chamber, and separately injecting the third molten material into the mold cavity with at least one of the injectors. The third molten material preferably remains separated from the first and second molten materials while in the receiving chamber. At least one injector preferably injects the third molten material into a different area of the mold cavity from the first and second molten materials. At least two of the first, second, and third molten materials may be identical molten metal alloys. The first, second, and third molten materials may be aluminum-based molten metal alloys, which may contain ceramic particulates. All three materials join along interfaces where the three materials meet in the mold cavity. The present invention is also a unitary compound cast product formed of at least two different casting materials and made by the method generally described hereinabove.
Further details and advantages of the present invention will become apparent from the following detailed description read in conjunction with the drawings.